The present invention relates to the detection of an object using an imaging device, or in particular to an object detecting method and an object detecting apparatus and an intruding object monitoring apparatus for automatically detecting an object intruding into the monitoring visual field by scanning a predetermined monitor area with the imaging device while changing the zoom setting of the zoom lens of the imaging device, changing the imaging direction of the imaging device or moving the imaging device, thereby changing the monitoring visual field.
An intruding object detecting apparatus using an imaging device such as a camera has been widely used. In recent years, however, demand has arisen for an intruding object detecting apparatus in which an intruding object such as a person or an automobile (vehicle) intruding into a monitoring visual field is detected not by a person watching the image displayed on a monitor, but automatically by the image signal input from the imaging device and a predetermined announcement or alarm is issued by appropriate means.
In order to realize such an intruding object detecting apparatus, first, an inputted image from the imaging device is compared with an image in which an object to be detected is not present, such as a reference background image, an input image which has been previously obtained or the like, through image processing and a difference therebetween is detected. For example, an input image and a reference background image in which an object to be detected is not present are compared with each other, a difference in the brightness or luminance value for each pixel is detected and an area of pixels that have large difference values is detected as an intruding object. This method for obtaining a difference is known as “subtraction method” and has been widely used.
The processing by the subtraction method will be explained with reference to FIG. 9. FIG. 9 is a diagram for explaining the principle of processing the object detection according to the subtraction method. Reference numeral 901 designates an input image, numeral 902 a reference background image, numeral 903 a difference image, numeral 904 a binarized image of the difference image 903, numeral 905 a subtractor, numeral 906 a binarizer, numeral 907 an person-like object picked up in the input image 901, numeral 908 an area generated by the subtraction, and numeral 909 an image of a cluster of the brightness values “255” binarized from the area 908 generated by the subtraction.
In FIG. 9, the subtractor 905 calculates the difference of the brightness value or luminance value between the input image 901 and the reference background ground image 902 for each pixel, and outputs the difference image 903. In the difference image 903, a person-like object 907 picked up in the input image 901, for example, is applied to the binarizer 906 as an area 908 where the difference has been generated between the reference background image 902 and the input image 901.
The binarizer 906 produces a binarized image 904 by determining the brightness value of each pixel less than a predetermined threshold value Th as “0” and the brightness value of the pixel not less than the threshold value Th as “255” (the brightness value of one pixel calculated as 8 bits). The person-like object 907 picked up in the input image 901 in this way is calculated as an area 908 for which a difference is generated by the subtractor 905, and detected by the binarizer 906 as an image 909 indicating a cluster of pixels having the brightness value of “255”.